1. Field of the Invention
The present invention relates generally to tape cassette reels and, more particularly, is directed to a tape cassette reel for use with a video tape cassette or the like.
2. Description of the Prior Art
In a video tape cassette, a pair of tape reels is housed within a cassette body and a magnetic tape is wound around the hubs of the pair of tape reels, with each end of the magnetic tape fixed to one of the respective reel hubs. Upper and lower flanges are formed on upper and lower ends of each reel hub so that the magnetic tape wound around the reel hub does not slip widthwise.
Prior art methods of molding the hub and flanges as a single piece suffered from limitations which allowed the tape to slip out of place widthwise on the hub (described below). To combat this problem, the upper and lower flanges are generally formed separately. More specifically, the upper flange is formed on the reel hub, with which the lower flange is integrally joined by means of an ultrasonic welding-process or the like. This process of molding the upper and lower flanges and then joining them complicates the manufacturing of the tape cassette reel.
In order to simplify the manufacturing process of tape cassette reels, the following tape reel is proposed in which the upper and lower flanges are molded together with the reel hubs, yet which prevents the magnetic tape from slipping off of the hubs. This proposed upper-and-lower-flange-integral-type tape cassette reel is disclosed in Japanese Laid-open Utility Model No. 58-22308.
In FIGS. 1 and 2, reference numeral 1 generally designates a tape cassette reel, molded of a synthetic resin or the like. Reference numeral 2 designates a reel hub around which a magnetic tape (not shown) is wound. Upper and lower flanges 4 and 3 are integrally molded to the upper and lower ends, respectively, of the reel hub 2.
The lower flange 3 is formed as a disk shape and guards the full length of the magnetic tape wrapped around the reel hub 2. Engaging teeth 5 are formed on the periphery of the lower flange 3 so that they may engage a locking member (not shown) provided at the cassette housing side, thereby locking the reel hub 2. The upper flange 4, on the other hand, is formed as a fan shape extending for a predetermined angle of arc around the circumference. In this embodiment, three upper flanges 4 are molded on the upper end of the reel hub 2 at intervals of about 120 degrees.
In this tape reel 1, opening portions 6 are formed through the lower flange 3 so as to allow portions of the metal mold to pass through and form the upper flanges 4.
As shown in FIG. 3, this tape cassette reel 1 is molded by injecting a melted synthetic resin into a cavity formed between upper and lower metal mold cores 7 and 8. Protruding portions 9 are provided on the lower metal mold core 7 so as to penetrate the lower flange 3. The horizontal cross-section of each of the protruding portions 9 is fan-shape, and the upper flange 4 is molded along the reel hub 2 by the protruding portion 9. Simultaneously, the protruding portions 9 cause the fan-shaped openings 6 to be formed in the lower flange 3. The protruding portions 9 of the metal mode core are provided with "drafts" to enable the upper and lower metal mold cores 7 and 8 to be released from each other with ease. Therefore, the upper flange 4 is formed slightly smaller in size than the opening portion 6.
In the tape cassette reel thus formed according to the prior art, the shape of the opening portion 6 of the lower flange 3 corresponds directly to the shape of the upper flange 4 so that, when the draft of the metal mold core and the strength of the lower flange are taken into consideration, the outer diameter of the upper flange 4 can not be increased more than a predetermined value. Because of this, when a magnetic tape T of the standard length is fully wound around the reel hub 2, as shown in FIG. 4, the upper flange 4 can not guard the whole wound length of the magnetic tape T.
When the tape cassette is shaken or vibrated inadvertently, the magnetic tape T wound around the reel hub 2 may slip past the upper flange 4 (see FIG. 5), causing the magnetic tape T to be damaged.